The present invention relates generally to imaging systems and more particularly to volumetric computed tomography.
A computed tomography or CT scan is a method of taking pictures of the inside of the body using an ultra-thin x-ray beam. As the x-ray beam passes through the body, it is absorbed by bones, tissues and fluid within the body, thereby varying resultant beam intensity. The intensity of the attenuated x-ray beam emerging from the body is measured by a device that converts x-ray beam photons into electrical signals. These signals are converted into a detailed picture.
A typical CT scanner, such as a third or fourth generation CT scanner, includes a gantry having an annular frame for rotatably supporting an annular disk about a rotation or scanning axis of the scanner. The disk includes a central opening large enough to receive a patient extending along the scanning axis, and the disk is rotated about the patient during a scanning procedure. An x-ray tube is positioned on the disk diametrically across the central opening from an array of x-ray detectors. As the disk is rotated, the x-ray tube projects a beam of energy, or x-rays, along a scan plane, through the patient, and to the detector array. By rotating the x-ray source about the scanning axis and relative to the patient, x-rays are projected through the patient from many different directions. An image of the scanned portion of the patient is then reconstructed from data provided by the detector array using a scanner computer.
In current third and fourth generation CT systems, clinical benefits are derived from acquiring partial or whole organ volumetric images during a single rotation of the gantry. To enable this, a detector having a large (e.g. greater than 80 cm) height or “z” direction (i.e. direction parallel to the scan rotation axis) is coupled to an x-ray source having a correspondingly wide “cone beam” angle to illuminate the entire detector.
During rotation, however, image artifacts are generated that affect the system when the cone angle reaches larger ranges. Various reconstruction schemes have been devised to eliminate these artifacts, but these require the x-ray source location to vary rapidly along the “z” direction as the x-ray source is rotated around the patient. Current x-ray tubes do not have this capability.
The disadvantages associated with current, CT systems have made it apparent that a new technique for CT scanning would be beneficial.
The new technique should allow x-ray source location to vary rapidly along the “z” direction as the x-ray source is rotated around the patient.
The new technique should also substantially eliminate image artifacts that affect the system when the cone angle reaches larger ranges. The present invention is directed to these ends.